Players in the leagues with caps are in a union. In exchange for the salary cap in question, they have things like minimum salaries, health benefits, guarantees about their working conditions, etc.

If you could guarantee that you and your colleague's salaries represented 50% of the revenue that the company collects, you would be in a much better place than many companies without a cap. If you and your colleague's could guarantee minimum salaries that can't be changed, you'd be in a good place. If you could guarantee working hours and conditions, you'd be in a good place.

Now, are there downsides? Absolutely! But those are the tradeoffs of union labor.